The purpose of the project is to examine measures of heart rate variability (HRV), continuously and noninvasively, in male and female alcoholics admitted for drinking cessation. The project serves to test the hypothesis that measures of HRV might serve to distinguish a priori sub-groups of patients at risk for more severe alcohol withdrawal in the absence of clinically apparent symptomatology. The peripheral manifestations of alcohol withdrawal syndrome (AWS) are characterized by rapidly changing autonomic influences. These may vary, minute to minute and hour to hour, depending on the severity and stage of AWS. Consequently, the development of HRV measures, which are relatively insensitive to non-stationarity of signal and could capture relevant data during short periods of measurement, was necessary prior to the protocol implementation. An algorithm, using phase-space decomposition, was developed that characterizes the type of noise exhibited in time-series measures such as inter-beat interval (IBI). In agreement with other workers using different methodologies, it was found that healthy subjects generate IBI time-series with noise characteristics between white noise and brown noise. The algorithm was found to be sensitive, distinguishing between healthy comparison subjects measured in an eyes open or eyes closed paradigm. Relatively short measurement times are required to extract the noise characteristics from the time-series within an acceptable degree of error. Relative insensitivity to non-stationarity of signal was demonstrated. We are now obtaining data from human subjects admitted for treatment of alcohol withdrawal syndrome. Since we found that alcoholic subjects had IBI time-series which were significantly less complex (as measured by H) than healthy comparison subjects, we would like to determine whether abstention from alcohol use for a period of 4 to 6 weeks results in a change of the complexity measure back to baseline (as defined by healthy comparison subjects) or if the decreased signal complexity remains stable for a period of 4 to 6 weeks. Two mansucripts related to this work have been submitted for peer review.